/* @flow */

import {
  warn,
  remove,
  isObject,
  parsePath,
  _Set as Set,
  handleError,
  noop
} from '../util/index'

import {traverse} from './traverse'
import {queueWatcher} from './scheduler'
import Dep, {pushTarget, popTarget} from './dep'

import type {SimpleSet} from '../util/index'

let uid = 0

/**
 * A watcher parses an expression, collects dependencies,
 * and fires callback when the expression value changes.
 * This is used for both the $watch() api and directives.
 */
export default class Watcher {
  vm: Component;
  expression: string;
  cb: Function;
  id: number;
  deep: boolean;
  user: boolean;
  lazy: boolean;
  sync: boolean;
  dirty: boolean;
  active: boolean;
  deps: Array<Dep>;
  newDeps: Array<Dep>;
  depIds: SimpleSet;
  newDepIds: SimpleSet;
  before: ?Function;
  getter: Function;
  value: any;

  constructor(
    vm: Component,
    expOrFn: string | Function,
    cb: Function,
    options

?: ?
  Object
,
  isRenderWatcher
?:
  boolean
) {
  this
.
  vm = vm

  if(isRenderWatcher) {
    vm._watcher = this
  }

  vm
.
  _watchers
.

  push(

  this
)

  // options
  if(options) {
    this.deep = !!options.deep
    this.user = !!options.user
    this.lazy = !!options.lazy
    this.sync = !!options.sync
    this.before = options.before
  }

  else {
  this
.
  deep = this.user = this.lazy = this.sync = false
}
this.cb = cb
this.id = ++uid // uid for batching
this.active = true
this.dirty = this.lazy // for lazy watchers
this.deps = []
this.newDeps = []
this.depIds = new Set()
this.newDepIds = new Set()
this.expression = process.env.NODE_ENV !== 'production'
  ? expOrFn.toString()
  : ''
// parse expression for getter
if (typeof expOrFn === 'function') {
  this.getter = expOrFn
} else {
  this.getter = parsePath(expOrFn)
  if (!this.getter) {
    this.getter = noop
    process.env.NODE_ENV !== 'production' && warn(
      `Failed watching path: "${expOrFn}" ` +
      'Watcher only accepts simple dot-delimited paths. ' +
      'For full control, use a function instead.',
      vm
    )
  }
}
this.value = this.lazy
  ? undefined
  : this.get()
}

/**
 * Evaluate the getter, and re-collect dependencies.
 */
get()
{
  pushTarget(this)
  let value
  const vm = this.vm
  try {
    value = this.getter.call(vm, vm)
  } catch (e) {
    if (this.user) {
      handleError(e, vm, `getter for watcher "${this.expression}"`)
    } else {
      throw e
    }
  } finally {
    // "touch" every property so they are all tracked as
    // dependencies for deep watching
    if (this.deep) {
      traverse(value)
    }
    popTarget()
    this.cleanupDeps()
  }
  return value
}

/**
 * Add a dependency to this directive.
 */
addDep(dep
:
Dep
)
{
  const id = dep.id
  if (!this.newDepIds.has(id)) {
    this.newDepIds.add(id)
    this.newDeps.push(dep)
    if (!this.depIds.has(id)) {
      dep.addSub(this)
    }
  }
}

/**
 * Clean up for dependency collection.
 */
cleanupDeps()
{
  let i = this.deps.length
  while (i--) {
    const dep = this.deps[i]
    if (!this.newDepIds.has(dep.id)) {
      dep.removeSub(this)
    }
  }
  let tmp = this.depIds
  this.depIds = this.newDepIds
  this.newDepIds = tmp
  this.newDepIds.clear()
  tmp = this.deps
  this.deps = this.newDeps
  this.newDeps = tmp
  this.newDeps.length = 0
}

/**
 * Subscriber interface.
 * Will be called when a dependency changes.
 */
update()
{
  /* istanbul ignore else */
  if (this.lazy) {
    this.dirty = true
  } else if (this.sync) {
    this.run()
  } else {
    queueWatcher(this)
  }
}

/**
 * Scheduler job interface.
 * Will be called by the scheduler.
 */
run()
{
  if (this.active) {
    const value = this.get()
    if (
      value !== this.value ||
      // Deep watchers and watchers on Object/Arrays should fire even
      // when the value is the same, because the value may
      // have mutated.
      isObject(value) ||
      this.deep
    ) {
      // set new value
      const oldValue = this.value
      this.value = value
      if (this.user) {
        try {
          this.cb.call(this.vm, value, oldValue)
        } catch (e) {
          handleError(e, this.vm, `callback for watcher "${this.expression}"`)
        }
      } else {
        this.cb.call(this.vm, value, oldValue)
      }
    }
  }
}

/**
 * Evaluate the value of the watcher.
 * This only gets called for lazy watchers.
 */
evaluate()
{
  this.value = this.get()
  this.dirty = false
}

/**
 * Depend on all deps collected by this watcher.
 */
depend()
{
  let i = this.deps.length
  while (i--) {
    this.deps[i].depend()
  }
}

/**
 * Remove self from all dependencies' subscriber list.
 */
teardown()
{
  if (this.active) {
    // remove self from vm's watcher list
    // this is a somewhat expensive operation so we skip it
    // if the vm is being destroyed.
    if (!this.vm._isBeingDestroyed) {
      remove(this.vm._watchers, this)
    }
    let i = this.deps.length
    while (i--) {
      this.deps[i].removeSub(this)
    }
    this.active = false
  }
}
}
